Flash memory cells are often bulky and difficult to fabricate in a desirable space due to complex geometries of the multiple gate layers used to form the control and floating gates. Accordingly, flash memory cells cannot generally be integrated as compact as other types of memory devices.
It is the general trend in the semiconductor market to manufacture devices with miniaturized dimensions, lower operation voltage, lower cost, higher speed, etc. The gate coupling ratio (GCR) between the floating gate and the control gate affects the operating voltage and device speed. The read/write method of a flash memory is affected by means of electrons transferring between the floating gate and the source/drain gate. Generally, the larger a gate coupling ratio between the floating gate and the control gate is, the lower required working voltage for operation will be. If floating gate-floating gate capacitance can be decreased, the interference issue will be suppressed. However, it is difficult to increase the overlapped area between the control gate and the floating gate in the conventional stacked gate structure. Accordingly the invention provides a method to fabricate a protruding floating gate, and the overlapped area between the control gate and floating gate will be increased.